package com.geeaks.learn.snowflake;

import org.apache.commons.lang3.RandomUtils;

public class Snowflake {
	
	long workerId;
	
	long datacenterId;
	
	long sequence = 0L;
	
	long twepoch = 1288834974657L;
	
	long workerIdBits = 5L;
	
	long datacenterIdBits = 5L;
	
	long maxWorkerId = -1L ^ (-1L << workerIdBits);
	
	long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	
	long sequenceBits = 12L;
	
	long workerIdShift = sequenceBits;
	
	long datacenterIdShift = sequenceBits + workerIdBits;
	
	long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
	
	long sequenceMask = -1L ^ (-1L << sequenceBits);
	
	private long lastTimestamp = -1L;
	
	private static volatile Snowflake snowflake;
	
	private Snowflake(long workerId, long datacenterId) {
		// sanity check for workerId
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}
	
	public static Snowflake getInstance(long workerId, long datacenterId) {
		if (snowflake == null) {
			synchronized (Snowflake.class) {
				if (snowflake == null) {
					snowflake = new Snowflake(workerId,datacenterId);
				}
			}
		}
		return snowflake;
	}
	
	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			throw new RuntimeException(
					String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
		}
		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0L;
		}
		lastTimestamp = timestamp;
		return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
	}
	
	public synchronized String nextId(int lenth) {
		if(lenth < 20 || lenth > 32) throw new RuntimeException("lenth must be great than 19 and less than 32!");
		int i = lenth - 19;
		Double begin = Math.pow(10, (i-1));
		Double end = Math.pow(10, i) - 1;
		return String.format("%s%s", this.nextId(),RandomUtils.nextLong(begin.longValue(), end.longValue()));
	}
	
	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}
	
	protected long timeGen() {
		return System.currentTimeMillis();
	}
}
